The present invention relates to flexible optical circuits. In particular, the present invention relates to flexible optical circuits having a backing layer, an adhesive coating and a release liner for attachment to a substrate such as an electronic printed circuit board.
The design of electronic circuits requires interconnections between devices for proper operation. With increased sophistication and operation speeds, design of functional interconnections requires careful engineering. The fastest data processing circuits and emerging technologies require large numbers of interconnects capable of carrying extremely high speed digital signals. Due to the increasing push for higher and higher speeds, engineers are facing fundamental limits in designing electronic interconnects.
In an attempt to handle higher speeds, interconnection technology has turned to optical interconnects for next generation circuits. Optical circuits have bandwidth capabilities orders of magnitude beyond electrical circuits, and are inherently immune to electrical interference. In some known designs, discrete fiber optic cables and fiber bundles are used to interconnect devices. Known standard fiber optic connection technology employed to connect optical fibers to devices are adequate for small numbers of interconnections. However, as optical circuit density grows, the physical bulk of cables and connectors make this approach unwieldy, especially for compact designs.
Attempts have been made to incorporate optical interconnects onto the surface of electronic circuit boards and substrates by constructing wave guides using optical polymers coated to the surface. An example of this is found in U.S. Pat. No. 5,521,992 to Chun, et al. The technology of the ""992 patent requires highly specialized tooling to generate each custom optical circuit thus standard circuit boards cannot be used. For simple circuits, tooling costs may be prohibitive. Waveguide fabrication is also difficult due to the small geometry of the guide regions, and optical quality of finished wave guides is poor due to limitations in optical polymer chemistry.
Flexible optical interconnect circuit packs are also known in the art. An example of this is found in U.S. Pat. No. 5,204,925 to Bonanni, et al. The known optical interconnect circuits have optical fibers bonded between two flexible substrates and have one or more optical connectors connected along the edges of the circuit pack. The connectors are then connected to one or more optical devices. These known devices are not adapted to bond to a substrate or circuit board.
The concept of using high bond strength pressure sensitive adhesive coated laminating films is not new. However, there are certain problems associated with the known adhesive coated films. For instance, it is often difficult to obtain accurate positioning during film use. Improper placement, static charge, and accidental contact can all contribute to misalignment and immediate bonding to the surface in undesired positions. Because of the immediate aggressive bonding, if alignment is off, the film is often destroyed or seriously damaged attempting to remove the film for repositioning.
One known solution to the above problem is to use a less aggressive adhesive so the user may remove or reposition the film in case of misalignment. This can result in poor long term adhesion. Another known solution is to use a partially cured adhesive material followed by a final curing process. This not only results in additional process step, but may be impractical for many applications. Yet another known solution is to prepare a surface wetted with a material that interferes with adhesion and then removing the wetting agent after final alignment is achieved. This approach can be messy and adds process steps.
There is a continuing need for flexible optical circuits capable of being applied to new circuit board designs without changing board design and fabrication techniques. There is also a continued need for a laminating film that allows for repositioning of the optical circuits to achieve proper alignment.
The present invention provides a flexible optical circuit applique that can be mounted on a circuit board without modifying the circuit board substrate or the electronic circuits. The optical circuit applique of the present invention is also repositionable. A method of manufacturing flexible optical circuit appliques is also provided.
A preformed fiber optic applique is provided having a backing layer. The backing layer or film, has an adhesive coating applied thereon. At least one optical fiber is routed and bonded to the adhesive layer providing a continuous optical signal path from one end to another. A releasable liner is releasably attached to the adhesive layer and positioned to cover the backing layer including the at least one optical fiber.
In one embodiment of the present invention, microstructures are provided on the backing layer. The microstructures are crushable structures that prevent the adhesive coating from immediately adhering to a substrate. This allows the film to be repositioned until proper alignment has been achieved. Upon the application of appropriate force, the microstructures will crush allowing the adhesive coating to bond the film to the substrate.
A method of fabricating the fiber optic appliques of the present invention is also disclosed. The method includes the steps of providing a supply of backing layer and applying an adhesive coating to the backing layer. At least one fiber is then provided and placed on the adhesive coating. Pressure is then applied to the at least one fiber to secure it to the backing layer.